import Callout from 'components/Callout';
import Steps from 'components/Steps';

# Next.js App Router Internationalization (i18n)

The Next.js App Router introduces support for [React Server Components](https://nextjs.org/docs/app/building-your-application/rendering/server-components) and unlocks [many benefits](/docs/environments/server-client-components) when handling internationalization on the server side.

## Getting started

If you haven't done so already, [create a Next.js app that uses the App Router](https://nextjs.org/docs/getting-started/installation).

`next-intl` integrates with the App Router, by using a `[locale]` [dynamic segment](https://nextjs.org/docs/pages/building-your-application/routing/dynamic-routes) so that we can use this segment to provide content in different languages (e.g. `/en`, `/en/about`, etc.).

Let's get started!

**Run `npm install next-intl` and create the following file structure:**

```
├── messages (1)
│   ├── en.json
│   └── ...
├── next.config.js (2)
└── src
    ├── i18n.ts (3)
    ├── middleware.ts (4)
    └── app
        └── [locale]
            ├── layout.tsx (5)
            └── page.tsx (6)
```

**Now, set up the files as follows:**

<Steps>

### `messages/en.json`

Messages can be provided locally or loaded from a remote data source (e.g. a translation management system). Use whatever suits your workflow best.

The simplest option is to add JSON files in your project based on locales, e.g. `en.json`.

```json filename="messages/en.json"
{
  "Index": {
    "title": "Hello world!"
  }
}
```

### `next.config.js`

Now, set up the plugin which creates an alias to import your i18n configuration (specified in the next step) into Server Components.

```js filename="next.config.js"
const withNextIntl = require('next-intl/plugin')();

module.exports = withNextIntl({
  // Other Next.js configuration ...
});
```

### `src/i18n.ts` [#i18nts]

`next-intl` creates a configuration once per request. Here you can provide messages and other options depending on the locale of the user.

```tsx filename="src/i18n.ts"
import {notFound} from "next/navigation";
import {getRequestConfig} from 'next-intl/server';

// Can be imported from a shared config
const locales = ['en', 'de'];

export default getRequestConfig(async ({locale}) => {
  // Validate that the incoming `locale` parameter is valid
  if (!locales.includes(locale as any)) notFound();

  return {
    messages: (await import(`../messages/${locale}.json`)).default
  };
});
```

<details>
  <summary>Can I move this file somewhere else?</summary>

This file is supported out-of-the-box both in the `src` folder as well as in the project root with the extensions `.ts`, `.tsx`, `.js` and `.jsx`.

If you prefer to move this file somewhere else, you can provide an optional path to the plugin:

```js filename="next.config.js"
const withNextIntl = require('next-intl/plugin')(
  // Specify a custom path here
  './somewhere/else/i18n.ts'
);

module.exports = withNextIntl({
  // Other Next.js configuration ...
});
```

</details>

### `middleware.ts`

The middleware matches a locale for the request and handles redirects and rewrites accordingly.

```tsx filename="middleware.ts"
import createMiddleware from 'next-intl/middleware';

export default createMiddleware({
  // A list of all locales that are supported
  locales: ['en', 'de'],

  // Used when no locale matches
  defaultLocale: 'en'
});

export const config = {
  // Match only internationalized pathnames
  matcher: ['/', '/(de|en)/:path*']
};
```

### `app/[locale]/layout.tsx`

The `locale` that was matched by the middleware is available via the `locale` param and can be used to configure the document language.

```tsx filename="app/[locale]/layout.tsx"
export default function LocaleLayout({children, params: {locale}}) {
  return (
    <html lang={locale}>
      <body>{children}</body>
    </html>
  );
}
```

### `app/[locale]/page.tsx`

Use translations in your page components or anywhere else!

```tsx filename="app/[locale]/page.tsx"
import {useTranslations} from 'next-intl';

export default function Index() {
  const t = useTranslations('Index');
  return <h1>{t('title')}</h1>;
}
```

</Steps>

That's all it takes!

<Callout>

**Next steps:**

<ul className="ml-4 list-disc">
  <li>Exploring `next-intl`? Check out the [usage guide](/docs/usage).</li>
  <li>
    Ran into an issue? Have a look at [the App Router
    example](https://next-intl-example-app-router.vercel.app/).
  </li>
  <li>
    Want to learn more about about using translations across the server and
    client? Check out [the Server & Client Components
    guide](/docs/environments/server-client-components).
  </li>
  <li>
    Wondering how to link between internationalized pages? Have a look at [the
    navigation docs](/docs/routing/navigation).
  </li>
  <li>
    Are you transitioning from the Pages to the App Router? Check out [the
    migration
    example](https://github.com/amannn/next-intl/tree/main/examples/example-app-router-migration).
  </li>
</ul>

</Callout>

## Static rendering

By using APIs like `useTranslations` from `next-intl` in Server Components, your pages will currently opt into [dynamic rendering](https://nextjs.org/docs/app/building-your-application/rendering/server-components#dynamic-rendering). This is a limitation that we aim to remove in the future, but as a stopgap solution, `next-intl` provides a temporary API that can be used to enable static rendering:

<Steps>

### Add `generateStaticParams` to `app/[locale]/layout.tsx`

Since we use a dynamic route segment for the `[locale]` param, we need to provide all possible values via [`generateStaticParams`](https://nextjs.org/docs/app/api-reference/functions/generate-static-params) to Next.js, so the routes can be rendered at build time.

```tsx filename="app/[locale]/layout.tsx"
// Can be imported from a shared config
const locales = ['en', 'de'];

export function generateStaticParams() {
  return locales.map((locale) => ({locale}));
}
```

### Add `unstable_setRequestLocale` to all layouts and pages

`next-intl` provides a temporary API that can be used to distribute the locale that is received via `params` in layouts and pages for usage in all Server Components that are rendered as part of the request.

```tsx filename="app/[locale]/layout.tsx"
import {unstable_setRequestLocale} from 'next-intl/server';

export default async function LocaleLayout({children, params: {locale}}) {
  unstable_setRequestLocale(locale);

  return (
    // ...
  );
}
```

```tsx filename="app/[locale]/page.tsx"
import {unstable_setRequestLocale} from 'next-intl/server';

export default function IndexPage({params: {locale}}) {
  unstable_setRequestLocale(locale);

  // Once the request locale is set, you
  // can call hooks from `next-intl`
  const t = useTranslations('IndexPage');

  return (
    // ...
  );
}
```

**Keep in mind that:**

1. The locale that you pass to `unstable_setRequestLocale` should be validated (e.g. in [`i18n.ts`](/docs/usage/configuration#i18nts)).

2. You need to call this function in every page and every layout that you intend to enable static rendering for since Next.js can render layouts and pages independently.

E.g. when you navigate from `/settings/profile` to `/settings/privacy`, the `/settings` segment might not re-render as part of the request. Due to this, it's important that `unstable_setRequestLocale` is called not only in the parent `settings/layout.tsx`, but also in the individual pages `profile/page.tsx` and `privacy/page.tsx`.

<details>
<summary>What does "unstable" mean?</summary>

`unstable_setRequestLocale` is meant to be used as a stopgap solution and we aim to remove it in the future [in case Next.js adds an API to access parts of the URL](https://github.com/vercel/next.js/discussions/58862). If that's the case, you'll get a deprecation notice in a minor version and the API will be removed as part of a major version.

That being said, the API is expected to work reliably if you're cautious to apply it in all relevant places.

</details>

<details>
<summary>How does unstable_setRequestLocale work?</summary>

`next-intl` uses [`cache()`](https://react.dev/reference/react/cache) to create a mutable store that holds the current locale. By calling `unstable_setRequestLocale`, the current locale will be written to the store, making it available to all APIs that require the locale.

Note that the store is scoped to a request and therefore doesn't affect other requests that might be handled in parallel while a given request resolves asynchronously.

</details>

<details>
<summary>Why is this API necessary?</summary>

Next.js currently doesn't provide an API to read route params like `locale` at arbitrary places in Server Components (see [`vercel/next.js`#58862](https://github.com/vercel/next.js/discussions/58862)). The `locale` is fundamental to all APIs provided by `next-intl`, therefore passing this as a prop throughout the tree doesn't stand out as particularly ergnomic.

Due to this, `next-intl` uses its middleware to attach an `x-next-intl-locale` header to the incoming request, holding the negotiated locale as a value. This technique allows the locale to be read at arbitrary places via `headers().get('x-next-intl-locale')`.

However, the usage of `headers` opts the route into dynamic rendering.

By using `unstable_setRequestLocale`, you can provide the locale that is received in layouts and pages via `params` to `next-intl`. All APIs from `next-intl` can now read from this value instead of the header, enabling static rendering.

</details>

### Use the `locale` param in metadata

In addition to the rendering of your pages, also page metadata needs to qualify for static rendering.

To achieve this, you can forward the `locale` that you receive from Next.js via `params` to [the awaitable functions from `next-intl`](/docs/environments/server-client-components#async-components).

```tsx filename="page.tsx"
import {getTranslations} from 'next-intl/server';

export async function generateMetadata({params: {locale}}) {
  const t = await getTranslations({locale, namespace: 'Metadata'});

  return {
    title: t('title')
  };
}
```

</Steps>
